Arrangement for simulating a reactive impedance



2 Sheets-Sheet 1 l F. CUR-ris ARRANGEMENT FOR SIMULATNG A REACTIVE IMPEDANCE Dec. 21, 1948.'

vFiledJune 21,1946

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ARRANGEMENT FOR SIMULATING A REAGTYIVE INI PEDANGE Filed June 2l, 1946 2 Sheets-Sheet 2 INVENTOR, LESLIE F. cumls,

TORNEY.

Patented Dec. 21, 1948 ARRANGEMENT FOR SIMULATING A REACTIVE IMPEDANCE Leslie F. Curtis, Great Neck, N. Y., assignor to Hazeltine Research, Inc., Chicago, Ill., a corporation of Illinois Application June 21, 1946, Serial No. 678,263

11 Claims. (Cl. 178-44) This invention relates to arrangements for simulating, within a selected range of frequencies, controllable substantially pure reactive impedances. Such an arrangement is particularly suited for use in an automatic-frequency-control system for controlling the frequency of an oscillator and, hence, will be described in that lconnection.

Pentode-tube arrangements and, to a .more limited extent, triode-tube arrangements, have been utilized to cause a controllable reactive current to now in the anode-cathode path of the tube for application to the terminals yof a resonant circuit to control the frequency thereof. In the usual reactance-tube arrangement, the output circuit of the tube is connected in shunt with the resonant circuit while the input circuit thereof is connected to the resonant circuit through a resistance-capacitance phase-shifting network which applies to the input circuit of the reactance tube an alternating potential which is nearly 90 out of phase with respect to the potential across the resonant circuit, and then only for very small input voltages. Likewise as the potential which is applied to the input terminals of the reactance tube from the phaseshifting network more nearly approaches the above-mentioned 90 relation, the control voltage developed by the phase-shifting network becomes smaller in value, so that the effectiveness of the phase-shifting network and the reactance tube are greatly reduced. Thus, the reactance tube never provides at its output electrodes a pure reactive current. Hence, the reactance tube draws a resistive or in-phase component of current from the resonant circuit which may undesirably load the latter to an extent which varies with the magnitude of the unidirectional biasing potential on the contr-ol electrode of the reactance tube. This, in turn, may unfavorably alter the amplitude of oscillations and hence the potential developed across the resonant circuit.

The magnitude of the real or in-phase component of the space current drawn by a triode reactance-tube arrangement from a resonant circuit is particularly large due to the relatively low anode-cathode resistance and'to a relatively large interelectrode capacitance of the triode, specically the anode control-electrode capacitance thereof. In some triode arrangements wherein attempts have been made unsuccessfully to utilize the anode control-electrode capacitance of the triode, the cathode control-electrode capacitance has inuenced the operation of the phase-shifting network so that an even greater of the tube.

in-phase component of spacecurrent results. The elect of the anode control-electrode capacitance, which heretofore has been considered undesirable in triode reactance-tube arrangements, and hence has been usually avoided rather than utilized, will be consideredin greater detail subsequently. As a result .of the above-mentioned shortcomings in triode reactance-tube control units, pentode reactance-tube arrangements have been utilized more extensively. The lastmentioned arrangements have proved, in general, to be more satisfactory because of the high anode-cathode resistance of the pentode and because of the shielding action afforded by the screen and the suppressor electrodes thereof which is effective materially to reduce the anode control-electrode capacitance. The space current of a pentode tube in such an arrangement is therefore more nearly in phase with the voltage applied to the input circuit of the pentode and, for many applications, the real component of thevspa-ce current is ordinarily neglected because of the high internal resistance of the tube. However, any prior resistance-capacitance phase-shifting network in combination with a pentode has not been capable of developing a space current having the desired relation with the voltage applied to the input circuit of the pentode so as to provide best performance. While possessing the advantages over triode arrangements mentioned above, known pentode reactance-tube units are not as sensitive as desired for many purposes. Furthermore, some pentode reactance-control units anord best operation only at a single frequency or over a very small range of frequencies. For certain purposes it may be desirable to employ a pentodetube arrangement having a comparatively high sensitivity over a relatively wide range of frequencies, While for other applications it may be preferable to utilize a triode reactance-tube arrangement to impress to controllable reactance on a resonant circuit to alter the frequency thereof.

Considering further certain aspects of a triode in a reactance-control unit, the anode controlelectrode capacitance of the triode is eiective to couple the control electrode of the tube to that portion of the circuit connected to the anode In arrangements of the type under consideration, the phase of the derived potential at the control electrode-cathode circuit of the triode differs from that at its anode-cathode circuitby less than 90 as determined by the elements of the usual phase-shifting network.

Consequently, the resultant efective potential on the input circuit of the triode is not in proper phase relationship to develop a space current in the triode which is in phase quadrature with the potential between the anode and the cathode of the tube. The anode-cathode circuit of the tube also carriesa 'urrentun phasemi'tvit'h Ythe voltage thereacross which is inversely proportional to the anode-cathode resistance of the tube. Components of space current due to the control electrode-cathode potentialand duev to the anode-cathode potential are therefore in 'such phase as undesirably to 7load the circuit connected between the anodeandrthe'cathode of the tube. Furthermore, the magnitude of the resistive or irl-phase component of this space ourrent varies with the magnitudenf .the `unidirectional biasing potential which is applied to the input circuit of the triode from a :frequencydetector unit, thus altering the potential across fjtheresonant circuit in a manner undesirably to inuericethe operation thereof. For example, *fthe oscillator including the resonant circuit may f become degenerative. Y

'j- If the phase of the input voltage or the output" 2.5

f through the resistive impedance to the junction of the reactive impedances at the control electrode a second high-frequency alternating potential having `the same frequency but opposite polarityto that of the rst alternating potential. Thevalues of the impedances are so selected that vthe network is'responsive to the rstand second alternating potentials to apply to the input electrodes a resultant alternating potential of a phase to cause the tube to provide at the outputnelec- 'trode's aspace'current which isv substantially in Fphase-quadrature relation to the rst alternat- 'fing potential over the selected range `of frequencies. Y

For a better understanding of the present invention, together with other and further objects thereof, reference is had tothe following description taken in connection with the accompanying drawings, and its scope will be'pointed out 'in fabove', now' isfinl phasev with the potential acrossJgo i'thefresonantcircuit'so that the oscillator is now regenerative? Thisv'un'desirably alters the output yvoltage of the'fbsciilator. y

Certain prior triode-type reactance-control ary"raf1'gnie'n'tis'"have partially compensated for ,the

f' undesirable influence of the an'ode control-elec- *trode capacitance Aof a'triode tube employed in Van" automatic-frequency-control system. However, theoperation of such arrangementshas not "been entirely satisfactory. y Some have been fre-"fil quen'cyselective or havenot been eective for 'fre- /quency-controlling purposes over a relatively #Iwide rangeof `freque'ncieslk v(.'lthers`have been '"difficult to adjust for proper operation or have f not 1been' sufficiently'sesitive for 'some purposes.V L

Itisan 'object vof the present invention, there- ""fregto provide anew and improved arrangement simulatingQwithin' a selected range of fref queiiciesga controllable substantially pureureacf "tive"inpedance,' which 'arrangement overcomes one-tor moreof vthe' above-mentionedv disadvantages and limitations of prior arrangements.

"lIt isanother objectpfth'e invention'to provide anew and improved arrangement for simulating,

'I withina selected range Yof frequencies, a controll'able substantially pure reactive impedance, Lwhich arrangement is substantially non-frequency selective over the aforesaid rangeof frequencies and is relatively easy to adjust for proper operation within 'that range of frequencies.

It is V-a further object of the invention to pror"vide an extremely sensitive arrangement utiliz- L ing an electron tubelof the triode type for simulating a controllable and substantially pure reactive impedance. f

` .In accordance with the invention, an arrange- Lrnent `for simulating, over a selected range of frequencies, a controllable.substantially pure reac- :"tive impedance comprises an electron tube hav- 'airgcontrolelectrode and cathode input electrodes the appended claims, 1 y

Referring now to the drawings, Fig, lis va circuit diagram, partly schematic, of a complete 'frequency-modulation carrier-signal receiver including an arrangement for simulating a control- -lablereactive impedance in accordance with a particular form of the present invention; Fig.

' 2a is a simplied schematic circuit diagram of an oscillator and an arrangement in accordance 'with the invention for controlling the frequency of the oscillator; Fig. 2b is the equivalent circuit diagram of the Fig. 2a arrangement; Fig.,3 vis a -vector diagram which is useful in conjunction Fig. l-arrangement comprising the instant invention; and Fig. 4 is a schematic circuit diagram of a modified form of the invention.

` Referring now more particularly to Fig. 1, there is represented schematically a complete frequency-modulation carrier-signal receiver having 'automatidfrequency control and embodying Ythe 'present invention in a preferred form. In general, the' receiver includes a radio-frequency amplier IU having an'input circuit connected to The frequency changer includes an oscillator portion or unit 2li 'tector I5 is' connected to the Mhthrough a control unit I9.

which Will be more fully described hereinafter. Connected Lin' cascade with the modulator I3, in the order "named," are an intermediate-frequency amplifier I 4 of lone or more stages, a frequency detector I5,an audio-frequency amplifierl of [one or more stages, and a sound reproducer I l.

lOn'e'of the output circuits of the frequency deoscillator unit v20 It`will be understood that the various units just -Vdescribed may', with the exceptionof the control 'unit' I9, be of conventional construction and op- ':."eration, Vdetails of which are well known inthe vl`artfrenderi'ng detailed description thereof unnecessary. Consideringbriefly the operation of the-*receiver as 1a whole", and neglecting for the `-trodes-'a -rst Vhigh frequency alternating-poten-"-75moment thev exact details of operation of the confrequency-modulated carrier' signal 'is intercepted by .the antenna system ,I I, I2, selected .and

amplified by -the radio-frequency amplifier I0, converted to an intermediate-frequency signal by the frequency changer including the modulator I3 and the oscillator 2.0, amplified in the intermediate-frequency ampli-fier I,4, and .detected rby the frequency detector I5, thereby to derive the audio-frequency modulation components. :The audio-frequency .components are, in turn, amplified in the audio-frequency' amplifier yII andare reproduced by the soundreproducer -I1 in a conventional manner.

It will be understood that the receiver preferably includes means, included in or preceding the detector I3, for eliminating or reducing the effects of undesired amplitude-modulation components in the reproduced signal. This lastnamed means may be of any type, insofar as the present invention is concerned and many such arrangements, per se, are well known to those skilled in the art. When the frequency of the signal applied by the oscillator 2U to the modulator I3 alters so that the intermediate-frequency output signals of the modulator I3 .deviate from. the frequency to which the intermediate-frequency amplifier I4 is tuned, a control voltage proportional to the extent of the deviation is applied by the frequency detector I5 to the control unit I9. The latter supplies a suitable reactive impedance in parallel with the tuned circuit'of the oscillator 20 which is effective to correct the frequency of the output signal thereof'so that the intermediate-frequency signal is adjusted automatically to a frequency near its proper value. In this manner any inaccuracies in the tuning of the receiver are corrected as well as any frequency drift of the oscillator 20.

Referring now more particularly to the portion of the system embodying the present invention, the control unit I9 for simulating, over` a selected range of frequencies, a controllable substantially pure reactive impedance comprises an electron tube 2I effectively of --the triode type,pref-` erably, a high mutual-conductance triode. Triode 2I includes input electrodes which comprise a control electrode 22 and a cathode 23 and output electrodes which comprise an anode 24 and the cathode 23. A controllable reactive impedance is developed between the output electrodes in a manner to be explained subsequently. The control electrode 22 of triode 2I is connected to an output circuit of the frequency detector I5 through the series combination of `filter resistors"`l 26 and 21, and a unidirectional source of biasing potential 23. A filter condenser 29 is coupled between the junction of the resistors 26- and 21 and ground. The control electrode `.22 vis also connected to the grounded cathode 23 through an adjustable condenser 30 which'includes the inherent capacitance between those electrodes. A condenser 32 is connected between the anode 24 and the control electrode 22 of tube 2I to couple the control electrode to a first high frequency alternating-potential source which will be described subsequently. This capacitance is represented by broken lines since it may be comprised in whole or in part by the inherent interelectrode capacitance of the tube. l This capacitance has a substantial value over the operating range of frequencies of unit I9 since tube 2l is a triode. The first high frequency alternating potential has a frequency within the operating range of frequencies of unit I9 and comprises the .cathode 23 of triode 2 I.

`6 parallel-resonant circuit including -a winding 33 and an adjustable condenser 34 of the oscillator 20.' One end of this parallel-resonant circuit is connected to the .anode of an electron tube 35 While the other end is connected to the grounded cathode .of the tube through a by-pass condenser 3B. The control electrode of tube 35 is coupled to an input terminal of the modulator I3 through a coupling condenser 31 and to the grounded cathode through a grid-leak resistor 38. One end of a reverse or feedback winding portion 43, which portion comprises a second high frequency alternating-potential source, is connected to the winding 3.3 and to a source of potential +B through a resistor 4 i, while the other end of wind- '.ing 4.0 is connected to the terminal of condenser 31 which is connected to an input terminal of the modulator I3.. Feedback winding 40. is magnetically coupled to winding 33 so that an alternating potential across the resonant circuit 33, 34 4is effective to induce a voltage across ywinding 4.4. f

" The arrangement for simulating a controllable reactive impedance also includes means for coupling the output electrodes 23 and 24 of the triode 2| to the resonant circuit 33, 34. This means comprises a first terminal 43 which is vcoupled to the anode electrode 24 of triode 2I ,50. The coupling means also comprises a second terminal 46 which is coupled to one end of `the resonant circuit 33, 34 through the by-pass condenser 35, and is directly connected to the The previously described d feedback winding 4D is poled in such a manner that it comprises a means for deriving from the first alternating-potential source 33, 34 a second high frequency alternating potential having the same frequency but opposite polarity to that of the first alternating potential.

The reactive impedance simulating arrange- ,ment of the instant invention also comprises a phase-shifting network, which is coupled to the feedback winding 4l), having at least one phased shifting resistive impedance and having phaseshifting reactive impedances comprised only by capacitance between the input electrodes of tube v2| and between the anode and control electrode thereof, so that the reactive impedances have -values varying in the same sense with frequency.

. These capacitances comprise the anode controlelectrode capacitance 32 of triode 2l and the .adjustable condenser 30 which is connected in 33, 34, and from the reverse winding 40, so as to apply to the input electrodes of tube 2l a re- .sultanrl alternating potential of a phase such as to cause vthe triode 2I to develop at its output electrodes 23, 24 a net space current which is substantially in phase-quadrature relation to the potential from the above-mentioned resonant circuit overthe selected range of frequencies. The phase relationship of this resulting alternat- 'ing potential will be treated in detailsubse- 41 due`to the n et 'potentialfrom the potential quently. l sources -TKe and `fron'rthe 'grid voltage eg, Nleads Referring now 'to Fig. 2a of the drawings, there the voltage -Ke'by less than"'90'as"il1ustratd. is-illustrated a simplified circuit diagram of the Current fwhiclr is the vector sum ofV currents `automatic-frequency-control 'arrangement of 'il 'and ii, as previously mentioned, leads the YFigi 1 including the essential elements ofrv the 'volta'gg by 90",A since reactive impedance :cat is oscillator and control tube circuit. Elements `entirely"capacitative. Voltage vector eg is the f'fcoresponding to those illustrated in the Fig'. 1 "resulting alternating potential developed by the farangement are identied by the same refernlphaseshifting Anetwork for application' VtoY the ime Characters- It W11 be apparent' presently)lw'cntrol' electrode ofjtube 2|, and wiu presenuy that this diagram is useful in considering the `bedfemrfin'strated'to be of a'phase to provide a voltage and current relations in the Various por- ""'s'pa'c current ip which is in phase-quadrature *tions of the reactive impedance-controlling ar- 'ilationshipto the potential e. l

rangement. The voltage represents the first It maybe demenstrated rathematieeuythat 'fhigh frequency alternating potential developedl "thefspace current ipof a triode', when operating "across the resonant circuit 33, 34 of the oscillator under' class A conditions, may be expressed bythe 20.** The voltage Ke which is the voltage kfcprnfiila induced in the feedback winding 40,*'has a magnie "tude which isa small fraction K ofthe potential L 'i=R-lgel 5) f e1 developed in the resonant circuit 33, 34, and-#20M y Y Y i has the same frequency as the last-mentioned whereinthe term g represents the mutual convioltagebut a polarity opposite thereto. The efv d uctanceo1 vthe triode andthe other terms are as f f e'ctive potential which r is applied to the input indicated above with reference to Fig. 2a. This electrodes of triode 2i is indicated as eg. Considrexpressionis alsorbelieved to be substantially corering now the currentsflowing in the variousf-25 rect `for class C operation. The `foregoing exbranches ofT `the phase-shifting network and pression may berewritten through the triode A2 l', the space current flowing through the tube`2l Ais designated ip; the current flowing through the condenser 32 is Vi1; the curyrent fiowing" through theadjustable condenserfBO f3'0' is i2; and the current flowing through there- "stor 41 is ia. kThe directionnofthe current ow isfassumed, for the purpose'of analysis ofthe "circuitoperation, to be as shown byI the arrows.

'Figl V26, which is the equivalent circuit forthe pRv=+Meg (7) Figlla arrangement, illustrates a circuit wherein-the tube 2l is replaced by its. equivalent gen- .wherein the term p. is the amplication factor of -theatube`V Accordingly-the internal potential drop in theanode-cathode circuit of the triode maybe expressed "Referring" again to Fig. 3 of the drawings, it eat'or eg in series with the internal resistance fwill'be seen that the internal potential drop z'pRp *I of the tube Rp vThe Sign of the equw'alentfgem comprises the vector sum ofthe voltage vectors i' erator peg is c onsideredpositive in sense vsince'theew anq "9F as expressed mEquatlon Tabove .Yhlch l-ycurrentin the tubehas been assumed to have a fmffybeV 'adjusted bYDIODeI SeleCOrl 0f the Cifdirection from anode to cathode. YIt will also be @uit 'components comprising the condense 30 noted that the lesmmntvv circuit 3 3, 34 and the v 'and -32 and the resistor 41 to be in phase quadra- `fee-beek Winding have been replaced bym r Vture'with the voltage e thus producing a space "equivalent generators. -The c'onder'isers in the'JA" Current i, which is also in phase quadrature with phase-shifting network are designated by the 'the Voltage the latter representing the pOlJenfreactances :rsoand :1:32. 'v f tialacross the resonant circuit of the oscillator 20 Considering now the ,operationof theFig. 2b Vof Figs. 1 and 2b. Condenser 30 is adjusted so arrangement for simulating a substantially puren that the desirable phase-quadrature relation is reactance, it is assumed that the current i1 isfo obtained at the range of the selected frequency that which flows through the reactive impedance range'.

- :13 to the'juncti'onpointwith reactiveiinpedance Thus any undesirable real component of space ist, It is also assumed that allthe current 'i2 `1is current, which would normally be present in a Atlfiatwhichflows through the reactancerrnand triode -reactancetube arrangement due to the that'-the current iris that whichflowsthfughmu anode,control-electrode capacitance of the tube, resistonVL `AccordingIy, 'the'follqir/ing' expresis compensated for in the triode arrangement of the instant invention by the described phasesiqn's win h id.'

' shiftingr network which utilizes the anode conn h @z "(1) trol-electrode capacitance of the tube 2|. It 'ez` jx30'2 I 'f"('2)-60 vwill alsobe observed in the vector diagram of '1 Y' Fig 3,'fthat the resultant alternating potential 'e-eg' 7*321'1 (3) eg, which is effective to provide at the output "d electrodes of the triode 2| of Figs. 1 and 2a.; a an substantially purely reactive current, differs from (4) 05 or leads the phase of the rst alternating potential e by slightly more than 90. Consequently this vresultant alternating potential which is ap- `plied -toythe'input electrodes of the triode 2l is elTectiVeto supply a real component of space current which is equal and opposite to that of the Re'ference'is now made to Fig.v 3 for;M afgrfaphi'cal representation of the operation of the Fig. 2b circuit.V VVVoltage vectors E and Kev extend in Qpp o site-A directions from the junction orrefer- 7o ence .point. Current Vector i1, which reprereal cd A,

'M m onent which would be t l-t d ,Sfmt-'Sim Current translated through thepa'pacl' the anodercathode circuit of the tubaayllzsteesanleI tw? eactafn $32 du? to the Voltage leads the bias -but'zivithout the influence of the particular vgltege e by ,11ear1y--..90".. Current .VeCtOIfalternating potential applied to the input elec- Y.which .represents the current carried by resistor 7:5A trodesbyrthe phaseshiftingnetwork. Also,- this 9 resultant alternating potentialV cg has a phase dissv placement with respect to the space current vector ip which is much less than 45. As a result of the last-mentioned phase relation, the resultant input voltage is effective to' produce a reactive space current having a magnitude which' is greater than that which would be developed' if a greater angular phase displacement existed". Consequently, an extremely sensitive reactance control arrangement results since the applica-v tion of a relatively small unidirectional biasing potential from a unit such as the` frequencyA detector l of Fig. 1, produces a material change in the magnitude of the reactive space current developed by the triode 2|, particularly when the triode 2l is of the high mutual-conductance type; In fact, an arrangement in accordance with the instant invention designed to operate in' lthe' region of 20 megacycles has proved to be atleast 4 times as sensitive as pentode reactance-tube arrangements.

In addition to being nonfrequency selective over the selected range of frequencies, a phase'-l shifting network in accordance with the instant invention may readily be adjusted by means ofthe condenser 33 to provide the proper'compensae tion necessary to develop a purely reactive s'pace current. While it is possible to adjust other' elements of the phase-shifting network to' effect theA desired compensation, adjustment of a compo' nent such as the condenser 30 in the' contr-ob' electrode cathode circuit of the tube 2l has proved to be most expedient. Once proper adjustment is made for one operating condition toprocure the desired phase angle between the voltag'e of the resonant circuit 33, 34 and the input poten'- tial eg of the triode 2l, the adjustment is also satisfactory for different values of unidirectional biasing potentials which may :be applied to" the' input circuit of triode 2l from the frequency de" tector I5 to alter the anode-cathode resistance of tube 2l and, hence, the magnitude of the reactive current developed thereby. Variations in the unidirectional potential applied' tothecontr'o'll electrode 22 of the triode 2l are not effective t0- alter the potential across the resonant circuit'Y 33, 34 and, hence, do not produce changes inthe amplitude of the oscillations or undesired frequency changes.

While applicant does not intend to limit the invention to any specic circuit constants, thev following circuit constants are given as' illustra-` tive of one embodiment of the invention con'- structed in accordance with the arrangement of Fig. 1.

Tubes 2| and 35-type 14W7 (connected as a triode, with screen and suppressor electrodes connected to the anode).

Condenser 38 (adjustable portion thereof)- 1.5 to 7 micromicrofarads.

Input capacitance of tube 2I-6.5 micromicro'- farads.

Condenser 32-4.5 mtcromicrofar'ads'.

Resistor 41H27() ohms.

K' (approximate value) 0.1;

Operating frequency-20 megacycles.

Fig. Llis a circuit diagram representing a modined form of an oscillator control unit which is essentially similar to the control unit I9 of Fig. 1, corresponding elements being designated by the same reference characters primed. In the Fig. 4 arrangement, the control tube comprises Y a pentode 60 including a screen electrode 6| which is 'connected to a source +B through a resistorV 62 and to ground through a bypass condenser 63.

The suppressorelectrode Ellis; directly connected to the grounded cathode 23. Because of the positive potential on the screen electrode 6I and the shielding action afforded by the suppressor electrode 64, the capacitance between the anode 24' and the control electrode' 22' of pentode B0 is extremely small. It is therefore necessary to augment this anodecontrol-electrode capacitance with a condenser 32 which has a capacitance' of the same order of magnitude as that of the triode 2l in the Fig. 1 embodiment. Condenser 32-I isr preferably of the variable type in order to permit adjustment of the sensitivity of control uri-it'- I9" and also the magnitude of the voltage' which is applied by the phase-'shifting network including the condenser 32 to the input circuit of the pentode 60 so to develop a pure reactive current between the anode and cathode electrodes thereof. Condenser need not be adjustable as in the Fig. 1 arrangement and may comprise,l in Whole or in part, the input capacitanceo'f the pentode 80.-

The operation is`r otherwise essentially similar to that of the Fig. 1 arrangement and Will not be repeated. The voltage' applied to the input circuit of the tube is exactly in phase O1'1`1ad'ra'' ture with that appearing between the output terminals thereof. Since reactance tube 60 i'sV a pentode, the expression for the Space' current does not contain the term is sensitive over a wider range of frequencies'tha is a conventional pentode reactance-control" unit;

Whilel there have been described what are at present considered to be the preferred embodi` ments of this invention, it will be obvious to those skilled in the art thatvarious changes and modications may be made therein without4 depart`' ing from the invention, and it is, therefore, aimed in the appended'claims tocover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. An arrangement for simulating,'over a* se'- lectedy range of frequencies,y a controllable sub'- stantially pure reactive `impedance comprising:

cathode' output electrodes between which said controllable reactive impedance is' developed;-

means for applying to said output electrodes a same sense withv frequency, said-network includ# ing means for applyingthrcugh said'resistiv'e'impedance to the' junction of said" reactive impedances at said control electrode a second highan electron tube having control electrode' and' cathode input electrodes and having anode and ..rst high-frequency alternating potential having' a frequency withinsaid range; and a phas'eeshifte" ing network having at least one phase-shifting resistive impedance and having phase-'shifting reactive' impedances comprised only by capaci-- i, tance between'said input electrodes' and between said anode and said control electrodesothat' said reactive impedances have values varying iny the*4 frequency. .alternating potential having .the-same' frequency butl opposite polarity to that of said first alternating potentiahthevalues of lsaid impedances being so selected that said network is responsive to said rst and to said second alternating potentials to apply to said input electrodes 2. An arrangement for simulating, over a selected range of frequencies, a controllable substantially pure reactive impedance comprising: an electron tube effectively of the triode type having control electrode and cathode input electrodes and having anode and cathode output electrodes between which said controllable reactive impedance is developed; means for applying to said output electrodes-a first high-frequency alternating potential having a frequency within said range; and a phase-shifting network having at least one phase-shifting resistive impedance and having-phase-shifting reactive impedances comprised only by capacitance between said input electrodes and the anode-control-electrode capacitance of said tube so that said-reactive impedances have values varying'in the same sense with frequency, said network including means for applying through said resistive impedance to the junction of said reactive impedances at said control electrode a second high-frequency alternatingpotential having the same frequency but opposite polarity to that of said firstalternating potential, the values of said impedances' being so selected that said network is responsive to said first and to said second alternating potentials to'apply to said input electrodes a resultant alternating potential of a phase'to 'cause'said tube to provide at said output electrodes a space current which is substantially in phase-quadrature relation to said first alternating vpotential over said selected range of frequencies.

3. An arrangement for simulating over a selected range of frequencies,` a controllable substantially pure reactive impedance comprisingi nselected range of frequencies, a controllablesbf;

put electrodes a yspace current whichV is substaritially in phase-quadrature relation to said rst alternating potential over said selected rrange of frequencies.

4. An arrangement for simulating, over `:a

stantially pure reactive impedance M- an electron tube of the high mutual conductance-` type having control electrode and cathode input-- 1electrodes and having anode and cathode output electrodes between which said controllableref;

active impedance is developed; means for apply-` ing to said output electrodes a rst high-frequency alternating potential having a frequency.

iwithin said range.; and ay phase-shifting network having at least one phase-shifting resistive iin-Q "pedances have values varying 1n the same sense with frequency, said network including means for applying through said resistive impedancetoff, the junction of said reactive impedances at saidwl lAcontrol electrode a second high-frequency alter- "nating potential having the same frequency but l opposite polarity to that of said first alternating potential, the values of said impedances beingl so selected that said network is responsive to said 3Q rst and to said second alternating potentials to apply to said input electrodes a resultant alternating potential of a phase to cause said tube to provide at said output electrodes a space cur--V rent which is substantially in phase-quadrature 35 relation to said first alternating potential over f saidselected range of frequencies. Y

5. An arrangement for simulating, Lover fa selected range of frequencies, a controllable substantially pure reactive impedance comprising:

40 an electron tube having control electrode and anelectron tube having control electrode and l cathode input electrodes 4and having anode and cathode output electrodes between which said controllable reactive impedance is developed;`

means for applying'to said output electrodes a first high-frequency alternating potential having' a frequency within said range; and a phaseshifting network having a phase-shifting resistive impedance coupled to said control electrodeand having phase-shifting reactive impedances com` prised only by capacitance` between said input electrodes and between said anode and said control electrode so thatsaid 'reactive impedances have values varying in the same sense with frequency, said impedances being coupled to forma" Y-connected phase-shifting network with said" control'electrode at the junction of `said net-y 1 work, said network including means forapplyl ing through said resistive impedance to said junction of said reactive impedances'a second' l high-frequency alternating potential having thel electrodes a resultant alternating potential of a phase to cause said tube to provideat said outcathode input electrodes and having anode andy -cathode output electrodes between which said f controllable reactive impedance is developed;v means for applying to said output electrodes a first high-frequency alternating potentialhav-f. ing a frequency within said range; and aplfiase -y I shifting network having at least oneV phaseshifting resistive impedance and havingrrphase--v shifting reactive impedances comprisedonly by ycapacitance between said input electrodesflan'd between said anode and said control-felectrodef:P` so that said reactive impedances have-values varying in the same sense with frequency,` said-f network including means fory applying-through?- said resistive impedance to the junction of s'ai'dffy reactive, impedances at said control electrode a,...

4values of said impedances being so selectedthat said network is responsive to said firstUar'idtL-,r-

said second alternating potentials to applyljto said input electrodes aresultantalternating',po;-z tential having a phase differing from .the ,phase .-f.-

of said first alternating .potential.byinorethan-f. 90 degrees to cause said tube to. providaat Said,-

output electrodes a space current which is substantially in phase-quadrature relation to said ,y first alternating potential over said selected 7014, range of frequencies.

6. An arrangement for simulating,` overa selected range of frequencies, a controllable fsubstantially pure reactiveimpeda'nce comprisingg; an electron tube having control electrode and cathode output electrodes between -which said controllable reactive impedance is developed; means for applying to said output `electrodes a first high-frequency alternating potential having a frequency within said range; and a phaseshifting network having at least one phaseshifting resistive vimpedance and -having phaseshifting reactive impedances ycomprised only -by capacitance between said input electrodes -and between said anode and -said control electrode so that said reactive impedances have values varying in the same sense with frequency, said network including means for applying through said resistive impedance to the junction of Asaid reactive impedances at said controlelectrode a second high-frequencyalternating potential hav-.- ing the same frequency but opposite polarity to that of said rst alternating potential, the `values of said impedances being so selected that said network is responsive to said rst vand to said second alternating potentials :to iapply .to said input electrodes a resultant alternating .potential of a phase to cause said tube uto provide Lat said output electrodes a space current which is substantially in phase-quadrature leading relation to said first alternating rpotential over said selected range of frequencies, thereby to provide a substantially pure inductive,reactancefacross said output electrodes.

7. An arrangementfor simulating-over a selected range of frequencies, a controllablevsubstantially pure reactive impedance comprising: an electron tube effectively of the triode type having control electrode and cathode input electrodes and having anode and cathode output electrodes between which said controllable reactive impedance is developed; means for applying to said output electrodes a first high-frequency alternating potential having a frequency within said range; an electron tube effectively of thetriode type having anode and cathode output electrodes between which said controllable reactive impedance is developed; means for applying to said output electrodes a first high-frequency alternating potential having a frequency within said range; and a phase-shifting network having at least one phase-shifting resistive impedance and having phase-shifting reactive impedances comprised only by capacitance between said input electrodes and the anode-control-electrode capacitance of said tube so that said reactive impedances have values varying in the same sense with frequency, said network including means for applying through said resistive impedance to the junction of said reactive impedances at said control electrode a second high-frequency alternating potential having the same frequency but opposite polarity to that of said first alternating potential, the values of said impedances being so selected that said network is responsive to said first and to said second alternating potentials to apply to said input electrodes a resultant alternating potential of a phase to cause said tube to provide at said output electrodes a space current which is substantially in phase-quadrature relation to said first alternating potential over said selected range of frequencies, said resultant alternating potential having a phase displacement with respect to said space current which is less than 45 degrees.

8. An arrangement for simulating, over a selected range of frequencies, a controllable substantially pure reactive impedance comprising: an electron tube effectively of thetriode type having control electrode and cathode input elecpedancescomprised only by capacitance between said :input electrodes and the anode-controlelectrode capacitance of said ytube so that said network has a substantially nonfrequency-selective response characteristic over said range of frequencies, said network including rvmeans lfor applyingithrough said resistive impedance to the junction of said reactive impedances at said'controlelectrode a second high-frequency alternating v4potential vhaving lthe same frequency -but opposite'polarity to that of said first alternating potentiaLthe-values of said impedances beingfso selected that said networkis responsive tosaid first and :to said second alternating potentials to apply to said input electrodes a resultant alternating potential of a phase to cause said tube to provide vat-said output electrodes a'space current Which'is `substantiallyin phase-quadrature relation -to said first alternating potential over said-selected range of frequencies.

9. -Anfarrangernent for simulating, over a selected range of frequencies, acontrollable -substantially pure reactive impedance comprising: an electron tube having control electrode and cathodeinput electrodes and having anode and cathode 'output electrodes between which said controllable reactive impedance is developed; means for applying to said output electrodes a first high-frequency alternating potential having a frequency within said range; and a phaseshifting network having at least one phaseshifting resistive impedance and having phaseshifting reactive impedances comprised only by capacitance between said input electrodes and between said anode and said control electrode so that said reactive impedances have values varying in the same sense with frequency, said network including a condenser coupled in shunt relation with said input electrodes to vsupplement the input interelectrode capacitance and including means for applying through said resistive impedance to the junction of said reactive impedances at said control electrode a second highfrequency alternating potential having the same frequency but opposite polarity to that of said first alternating potential, the values of said impedances being so selected that said network is responsive to said first and to said second alternating potentials to apply to said input electrodes a resultant alternating potential of a phase to cause said tube to provide at said output electrodes a space current which is substantially in phase-quadrature relation to said first alternating potential over said selected range of frequencies.

10. An arrangement for simulating, over a selected range of frequencies, a controllable usbstantially pure reactive impedance comprising: an electron tube having control electrode and cathode input electrodes and having anode and cathode output electrodes between which said controllable reactive impedance is developed; means for applying to said output electrodes a first high-frequency alternating potential having a frequency within said range; and a phaseshifting network having at least one phaseshifting resistive impedance and having phaseshifting reactive impedances comprised on1yfby in cluding means for applying through said resistive impedance to the junction of said reactive impedances at said control electrode a second high-frequency alternating potential having the same frequency but opposite polarity to that of said rst alternating potential, the values of said impedances being so selected that said network is responsive to said rst and to said second alternating potentials to apply to said input electrodes a resultant alternating potential of a phase to cause said tube to provide at said output electrodes a space current which is substantially in phasequadrature relation to said ilrst alternating po#V tenti-al over said selected rang-e of frequencies. 11. An arrangement for simulating, over a selected range of frequencies, a controllable substantially pure reactive impedance comprising: an `electron tube of the pentode type having control electrode and cathode input electrodes and having anode and cathode output electrodes between which said controllable reactive impedance is-vvdeveloped; means for applying to saidoutput electrodes a rst high-frequency alternating potential having a frequency within said range; and a' 4phase-shifting network having at least one phase-shifting resistive impedance and having phase-shifting reactivev --impedances comprised only. l'by capacitance between saidrinput electrodesv and between said anodev and said control electrode so that fsaid reactive impedances have values varying in the samelsense .with `frequency,.said

network includingra-'condenser in shunt relation With saidfanodef and said control electrode for.`

augmenting `theanode-control-electrodeY` vintere electrode capacitance and including meansk for applying through said resistive impedance tothe junction-'of said reactive impedances at said control electrode aA second high-frequency alternat-` ingypotential having the same frequency.V Jbut opposite polarity to that of said rst alternating potential, 'the values'y of said impedances being so r yselected `that-said network is responsiveato said -rst and to saidlsecond alternating potentials to apply to. said input electrodes a resultant alternating potential of a phase to cause said tube to, provide atV said output electrodes a space our@`L rentl which isy substantially in phase-quadrature relation YIto said instalternating potential over said selected range ofu frequencies, g f

., LESLIERCURTIS j REFERENCES CITED niet offthis-patent: f Y* l l UNITED erg-DES T11 The vfol-lowingAY references ,areV of` record in the Datev I Certicate of Correction Patent N o. 2,457,034. December 21, 1948.

LESLIE F. CURTIS It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 2, line 42, for the Words to controllable read a controllable; column 8, line 8, for resulting read resultant; column 13, line 40, claim 7, beginning With an electron tube strike out all to and including the Words and semi-colon said range; in line 45; column 14, line 65, claim 10, for the syllable and hyphen usb read sub; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case n the Patent Office.

Signed and sealed this 21st day of June, A. D. 1949.

[SEAL] THOMAS F. MURPHY,

Assistant ommz'ssz'oner of Patents. 

